05000499/LER-2005-004

LER-2005-004, Essential Cooling Water Inoperable Longer Than Allowed Outage Time

Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000
Event date:	7-11-2005
Report date:	11-30-2005
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability
4992005004R01 - NRC Website

I.�DESCRIPTION OF REPORTABLE EVENT

A. REPORTABLE EVENT CLASSIFICATION

This event is reportable pursuant to 10CFR50.73(a)(2)(i)(B) as a Condition Prohibited by Technical Specifications and 10CFR50.73(a)(2)(vii) as a Common Cause Inoperability of Independent Trains. STPNOC has determined, based on metallurgical analysis of the failed parts, that Essential Cooling Water (ECW) Train 2A was inoperable for an undetermined period of time. Since this condition developed slowly it logically existed for a period longer than the Technical Specification 3.7.4 Allowed Outage Time although the length of time can not be determined definitively. Even though there is no evidence of the time of inoperability STPNOC submits this report pursuant to 10CFR50.73(a)(2)(i)(B) as a Condition Prohibited by Technical Specifications. Inspections on ECW Train 2B on 15 August 2005 discovered a similar condition and inoperability. Since the two independent ECW Trains 2A and 2B were reasonably inoperable during the same period for the same cause this condition is also reportable per 10CFR50.73(a)(2)(vii) as a Common-cause Inoperability of Independent Trains.

B. PLANT OPERATING CONDITIONS PRIOR TO THE EVENT

Unit 2 operated in Mode 1 at full power for the duration of this event.

EVENT

When the first indications of the condition were noticed for ECW Train 2A due to through-wall leakage on 27 June 2005, ECW Train 2C was out of service, but functional, for routine scheduled traveling screen maintenance.

TIMES

In May 2005, cavitation damage was discovered in the slip-on flange immediately downstream of the Unit 1 Component Cooling Water (CCW) Heat Exchanger 1B ECW Return Throttle Valve, 1-EW-0064. Work requests were then initiated to inspect the component cooling water heat exchanger return throttle valves in all trains of both units.

11 On June 27, 2005, approximately three gallons per hour leakage was discovered from the flange downstream of 2-EW-0027. The leakage was from two discrete pinpoint flaws located in the carbon steel flange hub near the joint fillet weld of the pipe to the carbon steel flange hub. A subsequent operability evaluation performed on 29 June 2005 concluded that the ECW Train 2A was operable with the through wall leakage (CREE 05-8601-1). Compensatory actions were taken to monitor the leakage and limits were set for circumferential crack length at the outside surface of the flange. The 2-EW-0027 inspection and repair was rescheduled to the next available 2A train work week.

When the train 2A 2-EW-0027 throttle valve was removed on July 11, 2005, cracks were discovered in the aluminum bronze piping inside the downstream slip-on flange:

• The aluminum bronze pipe end had separated for about 34.5 inches along the heat affected zone of the pipe end to flange fillet seal weld. This separation was located where the disc of 2-EW-0027 entered the downstream flange. The total circumferential length of this fillet seal weld is about 93".

• The aluminum bronze pipe had a 17.6 inch long circumferential crack along the upper side of the heat affected zone of the external (lower) pipe to flange hub fillet weld. This crack was also located where the disc of 2-EW-0027 entered the downstream flange.

• There was a 3.5 inch long axial crack through the aluminum bronze pipe, connecting the 34.5 inch long pipe separation and the 17.6 inch long circumferential crack.

• Just past the end of the 34.5 inch separation, there was another 1.5 inch long separation of the aluminum bronze pipe end along the heat affected zone of the pipe end to flange fillet seal weld.

• There were three additional pipe end separations on the side of the pipe opposite the location of the 34.5 inch separation. These separations were 3.5, 2.5, and 1.8 inches long.

• Two through-wall cavitation impingement areas were located in the aluminum bronze pipe just below the pipe end to flange fillet seal weld. The through-Wall areas were located where each side of the disc of 2-EW-0027 just entered the downstream flange.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001) 2. DOCKET1. FACILITY NAME 6. LER NUMBER 3. PAGE 2005100411

• At the two through-wall cavitation impingement areas, pitting of the carbon steel slip-on flange extended to about one inch deep. Ultrasonic thickness readings taken from the outside of the flange at the hub below the bolting ring showed minimum remaining thickness of about 0.61 inches from an initial nominal thickness of 1.28 inches. Metal loss at this lower point was over about a two inch wide area.

• Dye-penetrant testing revealed five pinhole indications all within about a two inch area in the carbon steel flange hub at the heat affected zone of the external (lower) pipe to flange hub fillet weld. Two of these pinhole indications had active water leakage.

Inspection of the 2-EW-0027 valve and upstream flange revealed erosion wear of the aluminum bronze pipe where the valve disc entered the upstream flange and cavitation impingement damage to the valve body and travel stop. A segment of the valve's Tefzel seat ring was missing. The eroded areas maintained adequate thickness so that the structural integrity of the valve body was not challenged.

A second operability and reportability review was then performed to-assess the aluminum bronze pipe damage discovered in the downstream flange (CREE 05-8601- 16). The 17.6 inch long circumferential crack along the upper side of the heat affected zone of the external (lower) pipe to flange hub fillet weld exceeded NRC Generic Letter 90-05's allowed crack size limit of three inches. Flaw evaluations were performed for the aluminum bronze pipe using linear elastic fracture mechanics methodology and limit load methodology to determine maximum critical crack size and bending loads allowed prior to catastrophic pipe failure. The structural integrity of the pipe was never compromised as the calculated safety margins exceeded one. However, since the calculated safety margins were less than the ASME required margins, ECW Train 2A was declared inoperable.

After the downstream flange for Train 2A was replaced via an ASME code repair, the downstream flange for Train 2C was inspected and replaced via an ASME code repair.

The Train 2C flange had separation of the aluminum bronze pipe from the heat affected zone of the pipe end to flange fillet seal weld but no circumferential or axial cracking in the aluminum bronze pipe. This slip-on flange did have two through-wall locations where corrosion of the carbon steel flange undermined the aluminum bronze overlay at the gasket seating area, but no through wall leakage. The observed damage for ECW Train 2C was within previous structural integrity acceptance criteria for flaw evaluations and the condition was evaluated as meeting operability requirements.

11 On 15 August, the downstream flange for Train 2B was inspected. This flange had an approximately 30" long by three inches wide segment of the aluminum bronze pipe broken free. A segment of broken pipe recovered during the inspection (about twenty inches long by three inches wide) was lodged between the pipe outside diameter and slip-on flange inside diameter. The remainder of the segment (up to ten inches long by three inches wide) is unrecovered and may have traveled some distance in the return header towards the discharge structure. CR 05-10323 evaluates the system impact of the unrecovered aluminum bronze pipe segment(s). ECW Train 2B was also declared inoperable for the same reasons as ECW Train 2A.

See Table 1 for a summary of the inspections results, operability determinations and repairs for ECW trains.

E.� THE METHOD OF DISCOVERY OF EACH COMPONENT OR SYSTEM FAILURE,

OR PROCEDURAL OR PERSONNEL ERROR

The conditions in ECW Trains 2A and 2B were discovered after inspections were performed in Unit 1. The initial inspection in Unit 1 discovered cavitation induced erosion in the CCW Heat Exchanger outlet throttle valve configuration. As a result of this initial discovery STPNOC determined that inspection of all trains in both Units was appropriate. Of the six trains inspected, the conditions discovered in ECW Trains 2A and 2B did not meet operability requirements.

II.� COMPONENT OR SYSTEM FAILURES A.� FAILURE MODE, MECHANISM, AND EFFECTS OF EACH FAILED COMPONENT Cavitation pitting, circumferential cracking, secondary axial Cracking and pipe end to flange weld separations were discovered in the aluminum bronze pipe inside a slip-on flange immediately downstream of the Component Cooling Water Heat Exchanger 2A and 2B Essential Cooling Water (ECW) Return Throttle Valves. Structural integrity of the pipe could not be verified using the requirements of NRC Generic Letter 90-05, "Guidance for Performing Temporary Repair of ASME 'Code' Class 1, 2, and 3 Piping.

Because structural integrity could not be demonstrated, ECW Trains 2A and 2B were declared inoperable due to non-compliance with ASME Code requirements.

11

B. CAUSE OF EACH COMPONENT OR SYSTEM FAILURE

The cause of the damage observed in the pipe/flange assembly is cavitation impingement from the heavily throttled butterfly valve.

OF COMPONENTS WITH MULTIPLE FUNCTIONS

None

D. FAILED COMPONENT INFORMATION

The aluminum-bronze pipe has a nominal diameter of 30 inches and a nominal thickness of 0.25 inch. The pipe material is SB 169 CA-614 rolled and welded plate (6-8 percent aluminum) fabricated to SA-155 dimensional tolerances. The slip-on flange material is SA-105 carbon steel. The slip-on flange is welded to the 30-inch aluminum bronze pipe with fillet welds at both ends.� .

III.�ANALYSIS OF THE EVENT

A. SAFETY SYSTEM RESPONSES THAT OCCURRED

Not Applicable. Condition discovered during planned maintenance.

B. DURATION OF SAFETY SYSTEM TRAIN INOPERABILITY

STPNOC has determined, based on metallurgical analysis of the failed parts that ECW Train 2A was inoperable for an undetermined period of time that logically existed for a period longer than the Technical Specification 3.7.4 Allowed Outage Time. The length of time can not be determined definitively since the slow development of the condition provided no evidence of the time of inoperability. Inspections on ECW Train 2B on 15 August 2005 discovered a similar condition and inoperability. The length of inoperability can not be determined definitively for ECW 2B either since the slow development of the condition provided no evidence of the time of inoperability.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (1-2001) 2. DOCKET1. FACILITY NAME 6. LER NUMBER 3. PAGE 2005� 004� 1 C.� SAFETY CONSEQUENCES AND IMPLICATIONS Engineering analysis (APTECH calculation AES-C-5862-1, CR 05-8601-25) determined that the discovered condition on ECW Train 2A justified the acceptance criteria for both the upset and faulted conditions per the 2004 edition of the ASME Section XI pipe flaw acceptance criteria. STPNOC is committed to the 1989 version of the ASME code and used those limits to determine operability impact. Since ECW Train 2A was acceptable per the 2004 version of the code and since ECW Train 2C was considered operable, the safety function for the ECW system was met and the safety consequences were low.

A subsequent engineering analysis of the as-found condition of the aluminum bronze pipe carbon steel slip-on flange configuration of the ECW train 2A and ECW 2B flanges was performed (CR 05-8601-33). This analysis determined that the ECW pipe to flange assembly was capable of maintaining structural integrity during seismic events.

Replacement of the flanges resulted in 108 hours0.00125 days <br />0.03 hours <br />1.785714e-4 weeks <br />4.1094e-5 months <br /> of ECW Train 2A unavailability and 88 hours0.00102 days <br />0.0244 hours <br />1.455026e-4 weeks <br />3.3484e-5 months <br /> of ECW Train 2B unavailability. The increase in core damage risk accrued by this unavailability time was controlled within the limits of the Configuration Risk Management Program.

Probabilistic risk assessment sensitivity studies were performed assuming guaranteed flange failure due to a seismic event (CR Action 05-8601-31). Assuming a single ECW train will fail during a seismic event and that all components serviced by that ECW train will fail, the Change in Core Damage Frequency was 1.8E-08 per year and the Change in Large Early Release Frequency was 1.5E-09 per year. In a bounding analysis, assuming all ECW trains and all systems associated with ECW will fail during a seismic event, the Change in Core Damage Frequency was 1.3E-06 per year and the Change in Large Early Release Frequency was 1.3E-07 per year.

IV.� CAUSE OF THE EVENT The root cause is the failure to incorporate requisite inspection activities for ECW piping into station programs.

V.�CORRECTIVE ACTIONS 1. Rework affected piping and components in accordance with applicable codes and Piping Specification 5L019PS0004.

Train 1A EW0027�CR 05-7071-20�Due date: 1RE13 Train 1C EW0101 CR 05-7071-19 Due date: 1RE13 Train 1B EW0064�CR 05-7071-18�Due date: 1RE13 Train 2A EW0027 CR 05-8601-3 Completed Train 2B EW0064�CR 05-7071-12 �Completed Train 2C EW 0101 CR 05-7071-13 Completed 2. Provide design change package to allow Belzona or equivalent product that is resistant to cavitation damage to be coated on affected internal piping and component surfaces at the subject valves.

DCP� CR 05-8601-18�Completed 3. Develop Preventive Maintenance activities to inspect internal piping downstream of CCW heat exchanger outlet butterfly valves to monitor effectiveness of the Belzona product application in the reduction of any cavitation damage.

Unit 1� CR 05-8601-36�Completed Unit 2 CR 05-7601-37 Completed 4. Implement an erosion monitoring program for the ECW system or incorporate requisite inspection activities into existing programs.

CR 05-8601-35� Due Date: 1/17/06

SUPPORTING ACTIONS

1. Perform an engineering analysis of the actual aluminum bronze pipe carbon steel slip-on flange configuration with the as-found conditions of the ECW Train 2A and ECW Train 2B flanges.

CR 05-8601-33 � Completed 2. Contract with a hydraulics/piping consultant to perform a review of the system conditions of the Component Cooling Water Heat Exchanger ECW Return Throttle Valves and determine additional strategies to reduce or eliminate cavitation.

CR 05-8601-34� Due Date: 3/15/06 VI.� PREVIOUS SIMILAR EVENTS None.

Table 1 — ECW Inspection Summary Train Date Type of Indications Found Operability Type of Repair Inspected 1B 05/16/05 1. Through-wall penetration of the aluminum Operable *Non-Code Repair: The bronze pipe in two areas just below the pipe aluminum bronze piping was end to flange fillet seal weld. coated with Belzona material until a permanent Code repair2. Pitting into the carbon steel flange hub at can be performed.these through-wall penetration areas extended as deep as 0.75 inches.

1C 05/23/05 1. Through-wall penetration of the aluminum Operable *Non-Code Repair: A weld bronze pipe in two areas just below the pipe overlay was performed over the end to flange fillet seal weld. crack and a non-Code seal weld was performed over the2. Pitting into the carbon steel flange hub at separation area. The twothese through-wall penetration areas through-wall pipe penetration extended as deep as 0.78 inches.

areas were cut out and sections 3. The aluminum bronze pipe end had of aluminum bronze pipe were separated for about 20 inches along the used as filler and welded in heat affected zone of the pipe end to flange place. The aluminum bronze fillet seal weld. piping was coated with Belzona material until a permanent Code4. The aluminum bronze pipe had a 6 1/2 inch repair can be performed.long circumferential crack along the upper side of the heat affected zone of the external (lower) pipe to flange hub fillet weld.

1A 07/05/05 1. Through-wall penetration of the aluminum Operable *Non-Code Repair: A seal weld bronze pipe in two areas just below the pipe was performed over the end to flange fillet seal weld. separation area and the aluminum bronze piping was2. Pitting into the carbon steel flange hub at coated with Belzona materialthese through-wall penetration areas until a permanent Code repair extended as deep as 1.15 inches.

can be performed.

3. The aluminum bronze pipe end had separated for about 11 1/4 inches along the heat affected zone of the pipe end to flange fillet seal weld.

• Relief requests have been submitted for the non-code repairs on ECW Trains 1A, 1B and 1C.

Table 1 — ECW Inspection Summary (Continued) Train Date Type of Indications Found Operability Type of Repair Inspected 2A 07/11/05 See Section LD above. Inoperable ASME Code Repair: The slip­ on flange assembly was replaced with a new slip-on flange assembly and the pipe internals were coated with a cavitation resistant Belzona compound.

2C 07/25/05 1. Through-wall penetration of the aluminum Operable ASME Code Repair: The slip­ bronze pipe in two areas just below the on flange assembly was pipe end to flange fillet seal weld. replaced with a new slip-on flange assembly and the pipe2. Two through-wall locations where were coated with acorrosion of the carbon steel flange cavitation resistant Belzona undermined the aluminum bronze overlay compound.

at the gasket seating area with no through wall leakage.

3. The flange had separation of the aluminum bronze pipe from the heat affected zone of the pipe end to flange fillet seal weld but no circumferential or axial cracking in the aluminum bronze pipe.

2B 08/15/05 1. This flange had an approximately 30" long Inoperable ASME Code Repair: The slip­ by 3" wide segment of the aluminum on flange assembly was bronze pipe broken free. replaced with a new slip-on flange assembly and the pipe2. A broken pipe section recovered during were coated with athe inspection (approximately 20" long by cavitation resistant Belzona3" wide) was lodged between the pipe compound.

outside diameter and slip-on flange inside diameter.